Radio frequency distribution system



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July 31, 1934. c. c. SHUMARD RADIO FREQUENCY DISTRIBUTION SYSTEI Filed Feb. 2. 1932 MQCEM M INVENTOR CHARLES c. SHUMARD BY #g WV ATTORNEY 235 5253 E J w lllfllll IIII'II' Patented July 31, 1934 UNITED STATES rxamzne RADIO FREQUENCY DISTRIBUTION SYSTEM Charles C. Shumard, West Orange, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application February 2,

6 Claims.

My present invention relates to electrical distribution systems, and more particularly to an improved signal voltage amplifier adapted for use in a system for distributing signal modulated radio frequency energy. (14% I 1 15. o... t

In my copending application Serial No. 5 filed February 25, 1931 there has been disclosed a radio frequency distribution system particularly adapted for apartment houses, hotels and the like, wherein modulated radio frequency energy collected on a single antenna may be distributed to a plurality of translating devices, as receivers, located at points remote from the antenna. Specifically, there was disclosed in said copending application an improved arrangement for collecting signal modulated radio frequency energy, preferably in the broadcast range, and aperiodically distributing such collected energy to a plurality of remote, independent receiver devices, the distributing system utilizing a shielded cable consisting of a pair of conductors. Furthermore, there was disclosed in the aforesaid application a voltage power amplifier device adapted to be disposed between the aperiodic antenna and the distributing cable input.

The amplifier comprised two stages of radio frequency amplification one of the stages being aperiodically coupled to the antenna, while the other stage comprised a pair of electron discharge tubes connected in parallel. While a voltage amplifier, constructed as disclosed in said copending application, is satisfactory, it is often desirable to employ a stage of balanced amplification in the voltage amplifier. While a stage of pushpull amplification, in the voltage amplifier, would result in the balanced characteristic, it is well known that push-pull amplification involves higher transformation ratios, more diificult to achieve at radio frequencies, than a pair of tubes connected in parallel, whereby both arrangements receive the same signal input and are connected to the same output.

Accordingly, I have devised a stage of balanced amplification, for use in a signal voltage amplifier of a radio frequency distribution system, the amplification stage, additionally, possessing the amplifying property of a pair of tubes connected in parallel, and it may be stated, therefore, that it is one of the main objects of my present invention to provide such a stage of balanced amplification.

Another important object of the present invention is to'provide a signal voltage power amplifier adapted to be connected between an aperiodic source of signal energy and a radio frequency transmission line, which amplifier comprises a pair of tubes so connected with respect to said source and transmission line that while functioning with respect to power amplification, in a manner similar to a pair of tubes connected in 1932, Serial No. 590,333

parallel, it nevertheless is balanced electrically for each half stage.

Still other objects of the present inventionare to improve generally the simplicity and efficiency of radio frequency distribution systems, and to specifically provide a signal voltage amplifier for use in such a system which is not only reliable in operation, but economically manufactured and installed.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically one circuit arrange ment whereby my invention may be carried into effect.

Referring to the accompanying drawing which represents in schematic fashion enough of the present invention to enable any one skilled in the prior art to construct the same according to its principles, there is shown an energy collecting device 1. Although not specifically shown in the drawing, it should be understood that the collecting device ,Irgif a'fitenna, is usually mounted at a relativefy high point of the structure containing the plurality of receiver devices. For example, it may be mounted on the roof of the building containing the receivers.

The antenna 1 supplies the collected radio frequency energy to a plurality of translating devices, or receivers (not shown) which receivers are usually located in different apartments,

or in different rooms of the same apartment, or if desired, in different rooms of an hotel. Each receiver is coupled to one of a plurality of two wire aperiodic transmission lines, each line being generally denoted by the numeral 20. To preserve simplicity of description, only a single aperiodic transmission line is shown. The transmission line 20 is coupled to the common signal collector 1 through a voltage power amplifier unit 21.

Each voltage power amplifier 21 comprises a plurality of elements now to be described in detail, the amplifier being disposed between the antenna 1 and the input terminals 20' of the transmission line. It is pointed out that additional voltage amplifiers may be employed in put circuits of tubes 14 and 15 through an aircore radio frequency transformer generally denoted by the reference numeral 11. The transformer is wound in a particular manner, and it will be observed that the second stage of the power amplifier comprises the two tubes 14 and 15 having their control grids connected in such a manner that they are in phase relationship. However, the output circuits of the tubes 14 and 15 are coupled, by means of an air-core radio frequency transformer generally denoted by the reference numeral 16, in such a manner that electrical balancing for each half stage is secured.

In my copending application referred to above there has been disclosed a socket power unit adapted for connection to any commercial power line in order to provide energizing current for the cathodes, anodes and control electrodes of the tubes 13, 14 and 15. In order to preserve simplicity of description in the present application, the socket power unit has not been shown herein, but it is to be clearly understood that such a unit would be housed within the electrostatic shield 30, and would essentially comprise a power source transformer, a double wave rectifier tube, a filter system, all arranged in the usual and conventional manner well known to those skilled in the prior art, the cathodes of the tubes 13, 14 and 15 being supplied with alternating current for heating to emit electrons, and the anodes of the three tubes being supplied with filtered rectified current in the usual manner.

Accordingly, it is thought sufiicient to show the anodes of tubes 13, 14 and 15 as supplied with uni-directional current from a source B through leads 14. One of the latter leads is connected to the anode of tube 13 through the primary coil 11' of transformer 11. The other lead 14' is connected to the anode of tube 14 through one-half 16' of the primary coil of transformer l6, and the other half 16" is connected in a similar manner between the anode of tube 15 and the lead 14'.

The negative legs of each of the cathodes of tubes 14 and 15 are connected by a lead 2 to the negative leg of the cathode of tube 13. The cathode of tube 13 is grounded by connecting it, through a lead 2, to the shield 30. It is pointed out that the low potential terminal of the resistor 6 is similarly connected to the shield 30, and accordingly, such connection point 3 is hereinafter considered as a ground point to designate the fact that the shield 30 is maintained at ground potential.

It will be noted that the voltage power amplifiercomprises two stages of amplification, and that the air-core radio frequency transformer 11 has its primary coil 11' shunted by a radio frequency by-pass capacity 11". Furthermore, a radio frequency by-pass condenser 4 is connected between the lead 14' in series with the primary 11', and the grounded shield 30 in order to by-pass radio frequency currents around the source of anode potential B.

The control grid of each of tubes 14 and 15 is coupled to the primary coil 11 through an inductance coil. Specifically, the grid of tube 14 is coupled to the coil 11' through an inductance coil 5, while the grid of tube 15 is coupled to the coil 11' through an inductance coil 5', it being nptgdhggi egepithatithalowapotential terminals of each ofcoilsfiandjflare connected, and that they-are-bothwound in the same direction. Bothdcoilsfi -and 5 -have 1 1162;

low potential sides connected through a lead 6 to the grounded shield 30. It is to be understood, however, that any well known type of grid biasing device may be employed for securing bias of grids of tubes 14 and 15.

For example, in my aforesaid copending application, such grid bias is secured by connecting the grids of tubes 14 and 15 to a resistor in the cathode circuit of tube 13, and in that case, of course, the cathode of tube 13 would be considered grounded through the resistor. However, any other desired manner of biasing the grids of tubes 14 and 15 may be employed. The anode of tube 14 is connected to the high potential side of coil 16', and the anode of tube 15 is connected through a lead 7, to the high potential side of coil 16".

The terminals 20, to which the transmission line 20 is connected, are connected to the secondary coil 8 of the transformer 16, the secondary coil thus feeding into the transmission line. Shielding of the complete amplifier 21 is not necessary for stabilization, it only being actually necessary to shield the radio frequency transformers. However, it is preferred to shield the radio frequency portions of the circuits to the antenna lead-in in order to minimize stray pick-up.

The electrostatic shield 30 is, therefore, provided about the amplifier, and usually also includes the socket power unit. The output of the voltage power amplifier feeds into a standard, shielded, double-conductor, lead covered cable 20, functioning as a radio frequency transmission line. proximately 50 ohms. The construction of the line will not be described in detail, special reference being made to my aforesaid copending application.

It is believed sufiicient to point out that the transmission line comprises a central stranded copper wire, functioning as the antenna side of the transmission line, surrounded by a metallic sheath, preferably made of lead. Insulation is disposed between the sheath and the central copper wire, and a metallic ground strip, preferably made of copper, disposed between the insulated central conductor and the metallic sheath. Thus, the conductor 9 represents the antenna side of the transmission line while the conductor 10 represents the ground side of the line.

At desired points of the transmission line there are arranged receiver outlet taps. The numeral 50 designates an outlet tap, or box, comprising a in common,

The natural impedance of the line is apmetallic housing which is grounded by means a 18, preferably having a value of about 500 ohms.

The ground terminal G is connected by a lead 51' to the grounded conductor 10, and it is to be understood that the ground side of a radio receiver will be connected to the terminal G. The condenser 17 is used so that all sets may be operated mechanically the same, and electrically practically the same, from the transmission line as from an average antenna, and at the same time not affect appreciably either line conditions or other receivers operated on the line 20 when it would be connected, disconnected, or operated. The condenser also serves to isolate the receiver input circuits so far as direct current is concemed.

The resistor 18 is utilized so that in the case of receivers of which the input circuits are series tuned, or practically tune in the broadcast band either at the frequency of operation or at some other frequency, approximate short-circuit of the transmission line, depending upon the degree of tuning and the resistance of the circuit, may not occur. While there has only been shown one outlet tap 50 connected to the transmission line 20, it will be understood that a plurality of similar outlet taps may be employed. The last outlet on a transmission line usually embodies a terminating resistor connected between the grqund strip and the antenna conductor.

It is believed that the operation of the present invention will be clearly understood from the aforegoing description and the accompanying drawing, it being particularly pointed out that energy of various frequencies is collected by the aperiodic antenna circuit 1, is then amplified in the coupling stage including the tube 13, amplified energy being transferred from the coil 11' to each of coils 5 and 5'. The second stage of amplification comprises the tubes 14 and 15 having their grids coupled to the coil 11'. Usual push-pull operation is secured with the tubes 14, 15. The connections and windings of the transformers coupled to the tubes are both reversed on one of each double coil to provide a split output primary 16', 16'', and a split input secondary 5, 5'.

Advantages of this arrangement may be stated as follows:

(1) The split windings are balanced electrostatically to ground, and electrostatically and electromagnetically with respect to their primary or secondary windings as the case may be.

(2) Higher inductance values for each winding are available in a given space, or the space may be cut down for given inductive values. Higher inductive values give more uniform aperiodic amplification.

(3) Resistances of split windings may be kept the same by using different size wires; inductances and turn values are a compromise, but differ less the larger the relative radii.

While I have indicated and described a system for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the power organizaion shown and described, but that electrically equivalent modifications in the circuit arrangements, as well as in the apparatus employed, may be made without departing from the scope of my invention as set forth in the appended claims.

What I claim is:

1. In a radio frequency distribution system, an aperiodic antenna, a signal voltage amplifier coupled to the antenna, and including at least one stage consisting of a single tube, and a succeeding stage comprising a pair of tubes, a transmission line inductively coupled to the output circuit of each of said tubes in said succeeding stage, and means for electrically balancing each half stage of said succeeding stage to obtain uni- Lktliiiiilitll form amplification throughout the broadcast ran e.

2. In a radio frequency distribution system, an antenna, a signal voltage amplifier coupled to the antenna, and including at least one stage consisting of a single tube, and a succeeding stage comprising a pair of tubes, a transmission line inductively coupled to the output circuit of each of said tubes in said succeeding stage, and means for electrically balancing each half stage of said succeeding stage to obtain uniform amplification throughout the broadcast range, said means comprising secondary coil sections wound in the same direction in the common input circuit of the pair of tubes, and a split primary in the common output circuit of the pair of tubes.

3. In a radio frequency distribution system, an antenna, a signal voltage amplifier coupled to the antenna, and including at least one stage consisting of a single tube, and a succeeding stage comprising a pair of tubes, a transmission line inductively coupled to the output circuit of each of said tubes in said succeeding stage, and means for electrically balancing each half stage of said succeeding stage to obtain uniform amplification throughout the broadcast range, said means comprising a split secondary in the common input circuit of the pair of tubes, and a split primary in the common output circuit of the pair of tubes, the connections and windings being both reversed on one of each split coil.

4. In a radio frequency distribution system, an antenna, a signal voltage amplifier coupled to the antenna, and including at least one stage consisting of a single tube, and a succeeding stage comprising a pair of tubes connected in pushpull, a transmission line inductively coupled to the output circuit of each of said tubes in said succeeding stage, and means for electrically balancing each half stage of said succeeding stage to obtain uniform amplification throughout the broadcast range, said means comprising a split secondary in the common input circuit of the pair of tubes, and a split primary in the common output circuit of the pair of tubes, the connections and windings being both reversed on one of each split coil.

5. In a radio frequency distribution system, an aperiodic antenna, a radio frequency signal voltage amplifier coupled to the antenna, and including at least one stage consisting of a single tube, and a succeeding stage comprising a pair of tubes connected in push-pull, a radio frequency transmission line having a secondary coil inductively coupled to the output circuit of each of said tubes in said succeeding stage, and means for electrically balancing each half stage of said succeeding stage to obtain uniform amplification throughout the broadcast range.

6. In a radio frequency distribution system, an aperiodic antenna, a radio frequency signal voltage amplifier coupled to the antenna and including at least one stage consisting of a single tube and a succeeding stage comprising a pair of tubes connected in push-pull, a transformer coupling said stages having a secondary formed of two coil sections, means for maintaining the low potential end of said coil sections at ground potential, a two part radio frequency transmission line having a secondary coil coupled to primary coils connected in the output circuit of said pair of tubes and means for maintaining one part of said line at ground potential.

CHARLES C. SHUMARD. 

